This invention relates to a medical diagnostic ultrasound system and method for imaging contrast agents in tissues, organs and/or blood. In particular, continuous monitoring of a contrast agent infused target allowing for contrast enhanced periodic imaging is provided.
Contrast agents are injected or introduced into human or animal tissue organs and/or blood to enhance the contrast of ultrasonic images. Contrast agents may take various forms. For example, perfluorocarbon gas-filled microbubbles encapsulated by an albumin shell are used. These contrast agents provide strong reflection of ultrasonic energy.
Ultrasonic energy may destroy contrast agents. U.S. Pat. Nos. 5,560,364 and 5,685,310 disclose suspending ultrasonic transmissions for a period of time to avoid such destruction. Once ultrasonic transmission is resumed, the enhancement of contrast provided by the contrast agents is significant, but diminishes as imaging and resulting destruction continues. Using an ECG signal, interrupted two dimensional B-mode imaging was used to provide contrast enhanced images. However, by suspending ultrasonic transmission between the triggers, diagnostic information capturing all of the dynamics of the motion of the heart musculature valves and blood flow is not obtained.
In order to avoid losing information between triggered images, low power ultrasonic energy has been transmitted for generating two dimensional B-mode images in between the triggered images (high power). This low power imaging provides an indication of the location of the target tissue or organ while minimally destroying or interacting with the contrast agent. When the high power imaging is momentarily resumed, contrast enhancement remains visible. Transmit parameters other than power may be changed to avoid destruction of contrast agents, such as lower ultrasound line density, different frequency transmission and shorter transmit burst durations.
In this method, the images are generated using the same imaging mode, such as B-mode imaging. For example, triggered high powered B-mode images are generated with substantially continuous low power B-mode images. In one embodiment, a continuous two dimensional Doppler and B-mode image is generated with a triggered amplitude detected two dimensional contrast agent image. However, the lower power results in lower quality B-mode images.
Alternating between two different imaging modes may be desirable. Triggered B-mode imaging of the heart has been displayed with a substantially continuous pulse wave (PW) Doppler strip image. By positioning the PW gate in the heart chamber, the PW strip image revealed the time course of a contrast enhanced increase in the intensity of the Doppler data. The triggered B-mode image was displayed above the PW strip.
Another mode for imaging contrast agents is the M-mode (motion mode). For example, Doppler energy M-mode is sensitive to tissue perfusion.